1. Field of the Invention
The present invention relates generally to clinically fitting a prosthetic hearing device to a recipient, and more specifically, to perception-based parametric fitting of a prosthetic hearing device.
2. Related Art
Prosthetic hearing devices, such as hearing aids, middle-ear implants, Cochlear™ implants, auditory brain stimulators and other such devices have been developed to assist people who were born with or developed hearing impairments. For example, cochlear implants are designed to assist individuals who are profoundly deaf or severely hearing impaired, by enabling them to experience hearing sensation representative of the natural hearing sensation. (Cochlear™ implants are commonly referred as Cochlear™ prostheses, Cochlear™ devices, etc.; simply “cochlear implants” herein.) In most such cases, these individuals have an absence of or destruction of the hair cells in the cochlea that naturally transduce acoustic signals into nerve impulses which are interpreted by the brain as sound. The cochlear implant bypasses the hair cells by directly delivering to the auditory nerves electrical stimulation representative of the sound.
Cochlear implants have traditionally consisted of two parts, an external sound processor unit and an implanted receiver/stimulator unit. Typically worn on the body of the recipient, the external sound processor unit primarily detects external sound using an audio pickup device such as a microphone, and by processing the received sound using an appropriate speech processing strategy, converts the detected sound into a coded signal.
This coded signal is then sent to the receiver/stimulator unit which is implanted in, for example, the mastoid bone of the recipient, via a transcutaneous link. The receiver/stimulator unit then processes this coded signal to generate a series of stimulation sequences which are then applied directly to the auditory nerve via a series of electrodes positioned within the cochlea.
With improvements in technology the external sound processor and implanted stimulator unit may be combined to produce a totally implantable cochlear implant unit capable of operating without an external device. In such a device, a microphone or other audio pickup device would be implanted within the body of the recipient, for example in the ear canal or within the stimulator unit. Detected sound is directly processed by a speech processor within the stimulator unit, with the subsequent stimulation signals delivered without the need for any transcutaneous transmission of signals. Such a device would, however, still have the capability to communicate with an external device when necessary, particularly for program upgrades and/or implant interrogation, and if the operating configuration of the device required alteration.
Typically, following surgical implantation of a cochlear implant, the recipient must have the implant fitted or customized to conform to the specific physiology and needs of that recipient. This procedure, often referred to as programming or “mapping,” results in the creation of a collection of data commonly referred to as a “program” or “map.” A map contains a set of instructions for the sound processor, including the stimulation mode and sound processing strategy(ies) chosen for the recipient. The map also includes operational setting values such as a value corresponding to the lowest amplitude at which the recipient hears a sound, referred to as the threshold level, or T-level, and the maximum amplitude at which the recipient comfortably hears the sound, referred to as the comfort level, or C-level. The map is utilized by the sound processor to ensure stimulation from the implant provides the recipient with comfortable and useful auditory perception.
A fundamental aspect of programming a cochlear implant is the collection and determination of recipient-specific operational setting values such as the noted T- and C-levels. Such operational setting values vary for each stimulation channel and recipient. Measuring such recipient-specific settings requires an experienced clinician or audiologist to first present a stimulus to each stimulation channel of the recipient's cochlear implant, and then to measure or receive a resulting response.
Given that obtaining measurements for each stimulation channel is time consuming, and given that the measurement process is repeated over potentially a large number of channels, conventional programming techniques are a laborious task requiring the clinician to have much experience and expertise, while also requiring the recipient to provide adequate feedback. This is further compounded by the fact that the recipient's perception of a provided stimulus may change subsequent to the initial implantation and map creation. In some cases, the recipient's perception of a provided stimulus may stabilize months after implantation.